The membranes of cancer cells are believed to differ significantly from those of normal cell lines. The central theme of this project is the continued development and use of spin labeling in studies of membrane model systems and biological membranes, with the aim of understanding membranes of normal and malignant tissues. The spin labeling technique consists of introducing a nitroxide free radical into the system of interest and observing the spin label by electron spin resonance spectroscopy. In previous work we introduced new classes of lipid spin labels, determined the degree of orientation in stacked lecithin bilayers, performed a thorough study of motion along fatty acid chains, examined polarity effects in membranes, and studied proximity effects. The proposed research represents a continuation and expansion of these efforts, with an emphasis on lipid protein interactions. The main objective during the coming year is to test the generality of the boundary lipid concept.